366 
CHEMISTRY: S. J. BATES 
Values 0 the Ratio — / RT for the Undissociated Molecules 
Equivalents 
per liter 
LiCl 
NaCl 
1.263 
1.280 
1.305 
1.323 
1.343 
1.375 
1.394 
1.413 
1.446 
1.488 
KCl 
1.249 
1.262 
1.289 
1.305 
1.325 
1.350 
1.375 
1.396 
1.412 
1.432 
KNOs 
CuS04 
1.090 
1.091 
1.085 
1.067 
1.046 
1.025 
1.055 
0.001 
0.002 
0.005 
0.01 
0.02 
0.05 
0.1 
0.2 
0.3 
0.5 
1.334 
1.366 
1.390 
1.439 
1.500 
1.577 
1.728 
1.279 
1.281 
1.275 
1.246 
1.217 
1.159 
1.100 
The results in the table show that, even in solutions as dilute as 0.001 
normal, neither the ions nor the imdissociated molecules obey van^t 
Hoff's law, though with decreasing concentration both become more 
nearly normal. 
The osmotic pressure of the ions is less than that calculated from this 
law. This is true in every case except for solutions of Hthium chloride 
at 0.1 normal and above; hydration is doubtless the cause of this 
exception. 
It can be shown, moreover, that the behavior of the ions may be 
represented within the error of the freezing-point determinations by an 
equation of the form 
= RT(l-\-kCr) 
The results seem to justify the assumption that the osmotic pressures 
of the two ions in a solution of a di-ionic electrolyte are the same up to 
moderate concentrations. For example, the behavior of the chloride 
ion is within the experimental error the same whether calculated from 
the data for sodium chloride or from that for potassium chloride. 
The undissociated molecules have an osmotic pressure consider- 
ably greater than that calculated from van't Hoff's law. At moderate 
concentrations the various salts do not behave similarly. In the case 
of the chlorides the deviations continue to increase with the concen- 
tration, but in" that of the nitrates a maximum is reached about 0.02 
normal. This somewhat surprising result, that the behavior of the 
least hydrated is the most complex, is connected with the fact that the 
exponent n is for these salts a minimum at about 0.02 normal. 
For solutions more dilute than 0.01 normal and in some cases to a 
much higher concentration, an empirical equation of a form similar to 
that which holds for the ions expresses the relation between the osmotic 
